Sift
the self-rising flour and salt together in a bowl. In another bowl,
beat the unsalted buffer and sugar with an electric mixer until light
and fluffy. Beat in the eggs one at a time, beating each egg until
incorporated before adding the next. Mix in the vanilla extract and
lemon zest.

Gently beat the flour mixture into the buffer
mixture, one third at a time, alternating with half the milk and half
the lemon juice after each of the first 2 additions of flour. Beat until
just combined; do not over mix.

Fill the prepared cupcake liners
with batter 3/4 full, and bake in the preheated oven until a toothpick
inserted in the center comes out clean, about 17 minutes. Let the
cupcakes cool in the pans for about 10 minutes before removing them to
finish cooling on a rack.

To make the icing, beat the cream in a
chilled bowl with an electric mixer set on Low until the cream begins to
thicken. Add the confectioners sugar and lemon juice, a little at a
time, beating after each addition, until fully incorporated. Increase
the mixer speed to High, and beat until the icing forms soft peaks,
about 5 minutes. Spread on the cooled cupcakes. Refrigerate leftovers.